Trench cutting apparatus are well known in the art and in broad terms will normally comprise a body portion and ground contacting assembly on which the body portion is mounted. The ground contacting assembly allows the body portion to move over the ground surface (such as the seabed) and may comprise skids or endless articulated tracks. In the latter case, the trench cutting apparatus may be self propelled so that it can move itself (under operator control) over the ground surface. Steering means are also conventionally provided, such as means for adjusting the angle of the endless articulated tracks with respect to a nominally vertical axis.
Depending from the main body portion, the trench cutting apparatus has a trench cutting device of which various types are known. These include jetting apparatus and chain cutters. The particular trench cutting apparatus is selected in accordance with the anticipated ground conditions.
Further, known trench cutting apparatus can include arrangements for transferring the longitudinally extensive member into the trench. The longitudinally extensive member may, for example, be initially laid adjacent to the intended path of the trench and transferred into the newly-cut trench by a suitable manipulating or handling device provided on the trenching apparatus. In other variations, the longitudinally extensive member may be paid out from suitable apparatus, but will still require proper location in the newly formed trench by means of suitable handling apparatus of the trench cutting apparatus.
Known trench cutting apparatus are very successful in laying longitudinally extensive members over relatively long and substantially straight paths, or where the trench follows a curve of relatively great radius. However, there are circumstances in which problems arise.
Notably, it has become a common requirement for trench cutting apparatus to operate effectively where the radius of curvature of the intended trench is small. This requirement is pertinent in particular with respect trenches to be formed proximate to offshore wind turbines.
In prior art trenching vehicles the requirement for a trench of small radius of curvature causes an issue with product supports provided at either end of the trench cutting apparatus which determine the points of entry and exit respectively of the longitudinal member into and out of the trench cutting apparatus. Conventionally the product supports are designed to pick up and set down the product (i.e. the longitudinally extensive member) on the centerline of the trench cutting apparatus. Where the trench has a small radius of curvature, picking up and setting down the product on the centerline of the apparatus becomes impossible.
Another problem is the need to carefully align the trench cutting apparatus over the product (i.e. over the longitudinally extensive member) to ensure that product grabs which are provided on the trench cutting apparatus are in a position (relative to the product) so that the grabs can lift the product. In short multiple cable burial activities such as inter-array cables on offshore wind farms it is important that the trench cutting apparatus is capable of quickly loading the product to improve cycle time. Conventional trench cutting apparatus do not achieve sufficiently quick loading times.
A further problem with conventional trench cutting apparatus is the requirement to displace (typically to pivot or “butterfly”) the trench cutting device so that it moves out of the path of the longitudinally extensive member as the longitudinally extensive member is lifted into the trench cutting apparatus. Thus fouling of the trench cutting device by the longitudinally extensive member is avoided (as is damage to said member) but a delay to operations is thereby introduced.
Another problem lies in is the inability of the conventional trench cutting apparatus to reverse along the longitudinally extensive member, around bends, to a fixed structure from which the longitudinally extensive member extends. The fixed structure is typically a wind turbine base or foundation and, of course, may be one of several such bases in a wind farm. The longitudinally extensive member may in this case be a power or control cable or the like. The requirement for such reversing derives from the need to start trench cutting as close as possible to the fixed structure thereby to maximise the amount of the longitudinally extensive member buried by the trench cutting apparatus. That is, trenching should optimally start from as close as possible to the fixed structure, in order to minimise the requirement for additional protection of the portion of the longitudinally extensive member which cannot be buried in the trench.
The present invention seeks to overcome or at least moderate of alleviate some or all of the above described problems.
The present invention further seeks to provide a trench cutting apparatus capable of operating where the radius of curvature of the intended trench is relatively small.
The present invention further seeks to provide a trench cutting apparatus whereby the longitudinally extensive member can be safely and effectively mounted to the apparatus when the radius of curvature of the intended trench, into which it is intended that the longitudinally extensive member be laid, is relatively small.
Still further the present invention seeks to provide a trench cutting apparatus with which the longitudinally extensive member can be mounted to the apparatus without interference from, and without interfering with, the trench cutting device of said apparatus.
Still further the present invention seeks to provide a trench cutting apparatus which is capable of approaching closely to a fixed structure, such as a wind turbine base, while moving in a reverse direction whereby trenching can commence close to said fixed structure.
Further again, the present invention seeks to provide a trench cutting apparatus capable of following a longitudinally extensive member located on a ground surface, said member defining a path including relatively small radius curves, and more especially when said apparatus is moving in the reverse direction that is in a direction opposite to that associated with trench cutting operations).